The present invention relates to a semiconductor light emitting device, and more particular to a light emitting diode (LED) with transparent electrodes disposed alternatively to each other.
The semiconductor light emitting device is a semiconductor device which can be used to convert electrical energy into light. The semiconductor light emitting device is composed of semiconductor materials with different conductivity types such as n-type and p-type semiconductor material. In the n-type semiconductor materials, the electrons in the outer shell of atoms can move freely as the carriers of current. The n-type semiconductor materials include the elements of the V group such as phosphorous (P), arsenic (As), antimony (Sb), etc. The carrier in the n-type semiconductor material is the so-called donor. On the other hand, in the p-type semiconductor materials, the atoms possess holes because of lack of electrons, where the holes can also be the carriers. The p-type semiconductor materials include the elements of the III group such as aluminum (Al), gallium (Ga), indium (In), etc. The carrier in the p-type semiconductor material is the so-called acceptor.
As the n-type and p-type semiconductor materials joining to form a composite material, the electrons and the holes would redistribute in the composite material where the p-n junction is formed between the n-type and p-type materials. The carriers in the materials with different conductivity types would cross the p-n junction when the forward bias is applied to the electrodes on the composite material. In another word, the basic principle of the light emitting diode is that the holes in p-type material and the electrons in n-type material are combined in the neighborhood of the p-n junction and the energy is released in photons under forward bias.
FIG. 1A and FIG. 1B are the cross-sectional view and the top view of a conventional blue light emitting diode respectively. FIG. 1A is the cross-sectional view of FIG. 1B along the cross-section I-I for the conventional light emitting diode presented by Nichia Chemical Industries, LTD.
As shown in FIG. 1A, in the conventional blue light emitting diode 100, an n-type gallium nitride (n-GaN) 104 is provided on the surface of the sapphire substrate 102. A p-type gallium nitride (p-GaN) 106 for forming the p-type mesa is provided on the n-GaN 104 and covers a portion of the surface of the n-GaN 104. The upper surface of the p-type mesa 106 is covered completely by a p-type transparent metal electrode 108 of combined nickel/gold (Ni/Au) structure. An n-type bonding pad 110 and a p-type bonding pad 112 act as joints for electrical connection while wire bonding (W/B) performed, where the n-type bonding pad 110 is disposed on the exposed surface of n-GaN 104 and the p-type bonding pad 112 is located on the p-type transparent metal electrode 108.
As the top view of the conventional blue light emitting diode 100 shown in FIG. 1B, the p-type mesa 106 is located on the square n-GaN 104. The p-type mesa 106 covers a portion of the square surface of the n-GaN 104, and the p-type transparent metal electrode 108 covers the upper surface of the p-type mesa 106 completely. The n-type bonding pad 110 and the p-type bonding pad 112 are located on the diagonal of the square surface of the blue light emitting diode 100 respectively.
The n-type bonding pad 110 and p-type bonding pad 112 must be disposed for electrical connecting to the n-GaN 104 and p-GaN 106 respectively, since the transparent sapphire substrate is an electrical insulating substrate. The region of light emission is limited around the p-type bonding pad 112 due to the position of the n-type bonding pad 110 and p-type bonding pad 112 as the connection electrodes. The conductivity of the p-GaN 106 formed on the n-GaN 104 is worse on account of the characteristic on growth of p-type material. Thus the p-type transparent metal electrode 108 is disposed between the p-GaN 106 and the p-type bonding pad 112 for of current spreading. The conventional blue light emitting diode 100 can illuminate entirely as the current spread by the p-type transparent electrode 108 and flowing into the p-GaN 106.
Because of the bonding pads regarded as connection electrodes and the resistivity of the p-type transparent metal electrode 108, the lengths of current paths on the p-type transparent metal electrode 108 between the n-type bonding pad 110 and the p-type bonding pad 112 are different, which causes the non-uniform emission and other problems in the square light emitting diode 100. Furthermore, the light emitting efficiency of the conventional device is diminished since the light emitted from the device is obstructed by the n-type bonding pad 110 composed of thick oblique metal layer.
In view of the above, one aspect of the present invention is to provide a semiconductor light emitting device in which the characteristic of current spreading is improved by the configuration of electrodes and the property of materials. The semiconductor light emitting device is provided with an n-type transparent electrode and a p-type transparent electrode arranged alternatively to each other, which results in improvement of current spreading, decrease of the operation voltage, increase of the light emitting efficiency and the uniformity of the luminous figures.
In another aspect, the present invention provides a light emitting diode in which the current spreading is improved with the configuration of electrodes and the enhancement of the materials. An n-type transparent electrode and a p-type transparent electrode are arranged alternatively to each other on the light emitting diode to improve the current spreading, decrease the operation voltage, increase the efficiency and the uniformity of light emission.
In a further aspect, the present invention provides a blue light emitting diode in which the current spreading is uniform, the operation voltage is decreased, and the light emitting efficiency and the uniformity of luminous figures are increased. In the blue light emitting diode including n-GaN and p-GaN, there are an n-type transparent electrode and a p-type transparent electrode arranged alternatively to each other on the blue light emitting diode, an n-type bonding pad and a p-type bonding pad with smaller areas are disposed on the n-type transparent electrode and p-type transparent electrode respectively.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the present invention provides a semiconductor light emitting device. The semiconductor light emitting device includes a substrate covered by a first layer. Both a second layer and a first transparent electrode are disposed on the first layer to cover different portions of the surface and arranged alternatively to each other. A second transparent electrode is provided in contact with the second layer. A first bonding pad and a second bonding pad are disposed on the first and the second transparent electrodes respectively.
Moreover, according to the aspects of the present invention, a light emitting diode is disclosed, wherein the light emitting diode includes a transparent substrate, an n-type semiconductor layer, a p-type semiconductor layer, an n-type transparent electrode, a p-type transparent electrode, an n-type bonding pad and a p-type bonding pad. The p-type semiconductor layer and the n-type transparent electrode are provided on the n-type semiconductor layer and arranged alternatively to each other, where the n-type semiconductor layer is disposed on the transparent substrate. The p-type semiconductor layer and the n-type transparent electrode cover different portions of the n-type semiconductor layer respectively. The p-type transparent electrode is provided in contact with the p-type semiconductor layer. The n-type and p-type bonding pads are located on the n-type and p-type transparent electrodes respectively.
Furthermore, the present invention discloses a blue light emitting diode including a transparent sapphire substrate covered by an n-type gallium nitride layer. A p-type gallium nitride layer and an n-type transparent electrode are disposed on different portions of the n-type gallium nitride surface and arranged alternatively with each other. A p-type transparent electrode is provided in contact with the surface of the p-type type gallium nitride layer. An n-type and a p-type bonding pad are located on the n-type and the p-type transparent electrodes respectively.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.